Transmitter



Q March 9, 1943. w VAN ROBERTS 2,313,700

POWER SUPPLY TRANSMITTER Filed Oct. 31, 1941 70 Law TO ANODE INVENTOR WALTER v /v koafkrs BY I W ATTORNEY Patented Mar. 9, 1943 TRANSMITTER Walter van B. Roberts, Princeton, N. J assignor to Radio Corporation of America, a corporation of Delaware Application October 31, 1941, Serial No. 417,384- 12 Claims. 250-}7) 'The present invention relates to. radio transmitters and, more particularly, to an arrange-- mentjfor supplying power for the operation of. the oscillator employed. therein.

object of the present invention is to improve the operation of radio and telegraph transmitters.

. Another object of the present invention is the energization of an oscillator within a radio transmitter circuit without requiring a separate power supply.

IStill anotherobject is the provision of an arrangement for: keying an oscillator in a radio transmitter wherein the keying circuit maybe maintained at or near ground potential.

Still a further object of the present invention is the provision of meansfor controlling the bias on power amplifier tubes in a radio transmitter in accordance with the" keying of the master oscillator.

:As one step in attaining the foregoing objects, and others which may appear from the .following description, I insert a resistance in the negative lead of the power supply for the power amplifier tubes of a radio transmitter such that suiiicient bias for said amplifier tubes is obtained from the drop across said resistance to limit the anode dissipation of said tubes to an allowable valu'e'in the absence of excitation. As a second step, the space currentsupply for the exciting oscillator is also obtained from the voltage drop or the voltage drop across the resistor. This, as

mentioned previouslsuis arranged to be of such value as to protect the power amplifier tubes in their resting condition, that is, in the absense of excitation. With the key closed the oscillator space current path presents a greatly able operating bias 'on the power amplifier tubes in their working condition. Finally,as a third step, a resistor is provided in series with the spacecurrent path with the biasconnection at the junction. Thus, when. the key is closed, the

bias applied to the amplifier tubes is divided'by the ratio of the resistance of the space current path ltorthextotal shunt path across the first resistancazi If The present invention be more; fully. un-,

derstood by-reierence to the. following detailed: description, which is accompanied by a drawing in which reference numeral I indicates general-- ly a radio frequency power amplifier.

Amplifier l is composed, in the present example, of a pair of thermionic discharge tubes 2 and 5 connected in a push-pull relationship. The anodes oftubes 2 and 5 are connected to a tank circuit composed of inductance 6 and tuning condensers 3 and 4. The tank circuit is coupled to the desired load by means of a link cir cuit l. The anode power supply for tubes 2 and 5 is identified by the arrows labeled and An inductance capacity filter 9 is provided between the power supply and the space current circuits of the tubes of the transmitter.'

Across the output end of the filter 9 1s connected a pair of resistors II and I2 forming a potential divider circuit for supplying the screen grid voltages for tubes 2 and 5. The relative values of resistors II and I2 may be chosen in accordance with the principles set forth in my prior Patent #2218925, granted October 22, 1940, in order to prevent unnecessary current drain and to provide the best possible regulation. In the negative lead from the anode power supply to ground is inserted a resistor I5 which serves two purposes. One purpose is, of course, to supply a negative bias on the grids of tubes 2 and 5 with respect to their cathodes. Since the grids have a conductive connection to the end of resistor [5 which is connected to the negative lead from the anode power supply and the cathodes are grounded, the grids will be maintainedmore negative than the cathodes by the potential drop through resistor l5. The second purpose of resistor 15 will be described shortly hereafter.

The input circuit for tubes 2 and 5 includes inductance l6 and tuning condensers l1 and [8. By means of a link circuit 20, tank circuit 2| of an excitation oscillator 22 is coupled to the grids of tubes 2 and 5. The oscillator 22, has, as a frequency determining element, a crystal 23 in the grid circuit of tube 24. Tank circuit 2| is connected in series between the plate of tube 24 and the fixed contact of key 25. The moving contact arm of key 25 is connected to the positive end of resistor I5. The cathode of tube 24 is connected to the negative end of resistor l5 through resistor 26. i

. I As will be readily apparent, with key 25 open, the bias applied to'power amplifier tubes 2 and 5.is the full voltage drop across resistorj l5. With key 25 closed, however, the oscillator space current, passing through resistor 26 reduces the bias. This reduction operates in two ways because, in the first place, the space current path of. oscillator tube 24 shunting resistor l5 reduces the total biasing resistance and, in the second place, the drop across resistor 26 is equivalent to moving the grid return for tubes 2 and 5 to an intermediate point on resistor l5. By properly proportioning resistors l5 and26 it is possible to. operate tubes 2 and 5 at theirproperbias dur ing keying intervals and still to apply a sufficient bias during spacing intervals such that the plate dissipation of tubes 2 and 5 is well within allowable limits.

It will be noted that the moving arm of key 25 is at ground potential at all times. thus minimizing the danger of accidental contact with high potentials. Even the fixed contact is not dangerous since any current drawn therefrom to ground must pass through tube 24.

In a practical embodiment which I have constructed, utilizing'for tubes 2 and 5a pair out 813' tetrode tubes with an anode potential supply of 2000 volts, resistors if and I2 were given the value of 56,500 ohms and! 30,300 ohms. The operating screen voltage was thereby fixed at 400 voltswith a maximum of not over I volts. The exciting oscillator circuit utilized a pair of 6L6 tetrode tubes in parallel. Resistor I was given a value of '750 ohms. Resistor 25 was so proportioned as to give a bias on gridsof tubes 2' and 5 of 90 volts with the key closed. With key 24 open the bias on the grids of tubes due to the drop through resistor l5 was of the order of 75 volts which was sufficient to prevent excessive plate current.

WhileI have particularly shown and described several modifications of my invention, it is to be distinctly understood that my invention isnot limited thereto but that improvementswithin the scope of the invention may be made.

I claim? 1. In a high frequency system, an electron discharge device generator including an anode and a cathode, a thermionic discharge tube amplifier having electrodes coupled to said generator and having a gain control electrode and a cathode connected in a circuit including an impedance wherein a potential is developed" which biases said tube to such extent as tolimit the dissipation at the anode to an allowable value and means for including said impedance between the anode and cathode of said generator device for. suplying space current thereto and for lowering the bias on said gain control electrode.

2. In a radio transmitter, a thermionic discharge tube amplifier of high frequency oscillations, a thermionic discharge tube generator of high frequency oscillations for exciting said amplifier, connections for supplying energy' to said amplifier, one of said connections including a series resistor so arranged that the potential drop therethrough provides a negative bias to control electrodes of the tube in said amplifier sufficient to limit the space current through said tube to a predetermined value in the absence of excitation, connections from said resistor to said generator for supplying space current for said generator, one of said second mentioned connections including keying means, the space current of said generator serving to reduce the control electrode bias for said amplifier to a predetermined value in the presenceof excitation of saidamplifier.

3; In a radio transmitter, an amplifier of high frequency oscillations including at least one thermionic discharge tube including anode,

cathode and control grid electrodes, means for connecting the positive terminal of asource of energy to said anode, means for connecting said cathode to the negative terminal of said source of energy including a resistance connected in series relation between said cathode and said negative terminal, a connection from the negative end of said-resistance to the. control grid-of said tube, the potential drop through. said resistance serving as a bias on said control grid sufficient to limit the anode current of said tube to a predetermined value, a generator of high frequency oscillations coupled to the grid of said amplifier ,tube and including a thermionic discharge tube having a space. current therethrough, said space current pathbeing adapted to be intermittently connected across said resistance in accordance with signaling impulses, said space current serving. to. reduce the potential drop across said resistor.

4. In a radio-transmitter, an amplifier'of high frequency oscillations including at least one thermionic discharge tube, said tube including anode, cathode and control-grid'electro'des, means for connecting the positive terminal of a source of energy'to said anode; means for connecting said cathode to the negative terminal of said source of energy includinga resistance connected in series relation between said cathode and said negative terminal, a second: resistance connected at one end to the negative end of said resistance and at the other end to a control grid circuit of said tube, the potential drop through said first resistance serving asia bias on said control grid sufiicientto limit the anode current. of said tube to a predetermined value, a generator of high frequency oscillations coupled to the grid of. said amplifier tube and including a thermionic discharge tube havingra space current path therethrough, said space current path being adapted to be intermittently connected from said other end ofsaid' second resistance. to the other end of said first resistance in accordance with signaling impulses, said resistance and said space current path serving as a. potential divider across said first resistance whereby the control grid bias on said amplifier tube is reduced to a second pre-- determined value.

5; In a radio transmitter, an amplifier of high frequency oscillationsincluding a pair of thermio'nic discharge tubes connected in a push-pull relationship, each of said tubes including anode, cathode and control grid electrodes, means for connecting the positive terminal of a source of energy to said anodes, means for connecting said cathodesto the negative terminal of said source of energy including a resistance connected in series relation between said cathodes and said negative terminaLa connection from the negative end of said resistance to the control grid of said tubes, the potentialdrop through said resistance serving as a bias on said control grid sufiicient to limit the anode current of said tubesto a predetermined value, a generator of high. frequency oscillations coupled to the grid of said'amplifier tube and including a thermionici'discharge tube having a space current path therethrough, said space current path being adapted to be intermittently connected across said resistance in accordance-with signaling impulses, said space current serving to reduce the potential drop across said resistor.

6. In a radio transmitter, an amplifier of high frequency oscillations including a pair of thermionic discharge tubes connected in a push-pull relationship, each of said tubes including anode, cathode and control grid electrodes, means for connecting the positive terminal of a source of energy to said anodes, means for connecting said cathodes to the negative terminal of said source of energy including a first resistance connected in series relation between said cathodes and said negative terminal, a second resistance connected at one end to the negative end of said resistance and at the other end to a control grid circuit of said tubes, the potential drop through said resistance serving as a bias on said control grids suflicient to limit the anode current of said tubes to a predetermined value, a generator of high frequency oscillations coupled to the grids of said amplifier tubes and including a thermionic discharge tube having a space current path therethrough, saidpath being adapted to be intermittently connected from said other end of said second resistance to the other end of said first resistance in accordance with signaling impulses, said resistance and said space current path serving as a potential divider across said first resistance whereby the control grid bias on said amplifier tubes is reduced to a second predetermined value.

7. In a radio transmitter, an amplifier of high frequency oscillations including a pair of thermionic discharge tubes connected in a push-pull relationship, each of said tubes including an anode, a cathode and a control grid electrode, means for connecting the positive terminal of a source of energy to said anodes, means for connecting said cathodes to the negative terminal of said source including a resistance connected in series between said cathodes and said negative terminal, a connection from the negative end of said resistance to the control grids of said tubes, a generator of high frequency oscillations including a thermionic discharge tube having at least an anode and a cathode, a connection from the cathode of said generator tube to the negative end of said resistance, a connection including keying means connected from the anode of said generator tube to the positive end of said resistance, and means for exciting said amplifier from said generator, said resistance having such value as to bias the control grid of said amplifier tubes substantially to cut-ofi when said keying means is open, the anode-cathode path of said generator serving to reduce the potential drop across said resistor when said keying means is closed.

8. In a radio transmitter, an amplifier of high frequency oscillations including a pair of thermionic discharge tubes connected in a push-pull relationship, each of said tubes including anode, cathode and control grid electrodes, means for connecting the positive terminal of a source of energy to said anodes, means for connecting said cathodes to the negative terminal of said source and including a first resistance connected in series between said cathodes and said negative terminal, a connection from the negative end of said resistance to the control grids of said tubes, said connection including a second series resistance, a generator of high frequency oscillations including a thermionic discharge tube having at least an anode and a cathode, a connection from the cathode of said generator tube to the end of said second resistance remote from said negative terminal, a connection including keying means connected from the anode of said generator tube to the other end of said first resistance, and means for exciting said amplifier from said genei'ator, said first mentioned resistance having such value as to bias the control grids of said amplifier tubes substantially to cut-oil when said keying means is open, the anode-cathode path of said generator and said second resistance serving as a potential divider across said first resistance for reducing the bias on the control grid of said amplifier when said keying means is closed.

9. In a high frequency system, a first electron discharge device having anode, cathode and control electrodes, means for supplying space current for said device, a resistor connected between said means and the cathode of said device, the potential drop through said resistor serving to supply a predetermined negative bias to said control electrode, a second electron discharge device having a space current path adapted to be shunted across said resistor, said shunt decreasing said negative bias to another predetermined value.

10. In a high frequency system, a first electron discharge device having anode, cathode and control electrodes, means for supplying space current for said device, a resistor connected between said means and the cathode of said device, the potential drop through said resistor serving to supply a predetermined negative bias to said control electrode, a second electron discharge device having a space current path adapted to be shunted across said resistor, said shunt decreasing said negative bias to another predetermined value, and an output circuit of said second device being coupled to an input circuit of said first device.

11. In a high frequency system, a first electron discharge device having anode, cathode and control electrodes, means for supplying space current for said device, a resistor connected between said means and a cathode of said device, the potential drop through said resistor serving to supply a predetermined negative bias to said control electrode, an electron discharge oscillator having a space current path adapted to be shunted across said resistor in accordance with signalling impulses, said shunt decreasing said negative bias to another predetermined value.

12. In a high frequency system, a first electron discharge device having anode, cathode and control electrodes, means for supplying space current for said device, a resistor connected between said means and a cathode of said device, the potential drop through said resistor serving to supply a predetermined negative bias to said control electrode, an electron discharge oscillator having a space current path adapted to be shunted across said resistor in accordance with signalling impulses, said shunt decreasing said negative bias to another predetermined value, and an output circuit of said oscillator being coupled to an input circuit of said first device.

WALTER VAN B. ROBERTS. 

